Scientists analyzed the chemical elements in the faintest known galaxy, called Segue 1, and determined that it is effectively a fossil galaxy left over from the early universe. Stars form from gas clouds and their composition mirrors the chemical composition of the galactic gas from which they were born.
New work from a team of scientists including Carnegie's Josh Simon analyzed the chemical elements in the faintest known galaxy, called Segue 1, and determined that it is effectively a fossil galaxy left over from the early universe.
Astronomers hoping to learn about the first stages of galaxy formation after the Big Bang use the chemical composition of stars to help them unravel the histories of the Milky Way and other nearby galaxies. Using these chemical analysis techniques, the team was able to categorize Segue 1's uniquely ancient composition. Their work is published by Astrophysical Journal.
Stars form from gas clouds and their composition mirrors the chemical composition of the galactic gas from which they were born. Only a few million years after stars begin burning, the most-massive stars explode in titanic blasts called supernovae. These explosions seed the nearby gas with heavy elements produced by the stars during their lifetimes. The very oldest stars consist almost entirely of the two lightest elements, hydrogen and helium, because they were born before ancient supernova explosions built up significant amounts of heavier elements.
In most galaxies, this process is cyclical, with each generation of stars contributing more heavy elements to the raw material from which the next set of stars will be born. But not in Segue 1 — in contrast to all other galaxies, the new analysis shows that Segue 1's star formation ended at what would ordinarily be an early stage of a galaxy's development. Segue 1 likely failed to progress further because of its unusually tiny size.
"Our work suggests that Segue 1 is the least chemically evolved galaxy known," Simon said. "After the initial few supernova explosions, it appears that only a single generation of new stars were formed, and then for the last 13 billion years the galaxy has not been creating stars."
Because it has stayed in the same state for so long, Segue 1 offers unique information about the conditions in the universe shortly after the Big Bang. Other galaxies have undergone multiple supernova explosions since their formation. The first supernovae to blow up, from the most massive stars, produce elements like magnesium, silicon, and calcium. Later explosions of smaller stars primarily make iron. Segue 1's uniquely low iron abundance relative to other elements shows that its star formation must have stopped before any of the iron-forming supernovae occurred.
Written By: Science Daily
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